Cardiac arrythmias, and atrial fibrillation in particular, persist as common and dangerous medical ailments, especially in the aging population. In patients with normal sinus rhythm, the heart, which is comprised of atrial, ventricular, and excitatory conduction tissue, is electrically excited to beat in a synchronous, patterned fashion. In patients with cardiac arrythmias, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normally conductive tissue as in patients with normal sinus rhythm. Instead, the abnormal regions of cardiac tissue aberrantly conduct to adjacent tissue, thereby disrupting the cardiac cycle into an asynchronous cardiac rhythm. Such abnormal conduction has been previously known to occur at various regions of the heart, such as, for example, in the region of the sino-atrial (SA) node, along the conduction pathways of the atrioventricular (AV) node and the Bundle of His, or in the cardiac muscle tissue forming the walls of the ventricular and atrial cardiac chambers.
Cardiac arrhythmias, including atrial arrhythmias, may be of a multiwavelet reentrant type, characterized by multiple asynchronous loops of electrical impulses that are scattered about the atrial chamber and are often self propagating. Alternatively, or in addition to the multiwavelet reenetrant type, cardiac arrhythmias may also have a focal origin, such as when an isolated region of tissue in an atrium fires autonomously in a rapid, repetitive fashion.
A host of clinical conditions may result from the irregular cardiac function and resulting hemodynamic abnormalities associated with atrial fibrillation, including stroke, heart failure, and other thromboembolic events. In fact, atrial fibrillation is believed to be a significant cause of cerebral stroke, wherein the abnormal hemodynamics in the left atrium caused by the fibrillatory wall motion precipitate the formation of thrombus within the atrial chamber. A thromboembolism is ultimately dislodged into the left ventricle, which thereafter pumps the embolism into the cerebral circulation where a stroke results. Accordingly, numerous procedures for treating atrial arrhythmias have been developed, including pharmacological, surgical, and catheter ablation procedures.
It has been found that by mapping the electrical properties of the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy, it is sometimes possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions. Examples of catheter-based devices and treatment methods have generally targeted atrial segmentation with ablation catheter devices and methods adapted to form linear or curvilinear lesions in the wall tissue which defines the atrial chambers, such as those disclosed in U.S. Pat. No. 5,617,854 to Munsif, U.S. Pat. No. 4,898,591 to Jang, et al., U.S. Pat. No. 5,487,385 to Avitall, and U.S. Pat. No. 5,582,609 to Swanson, the disclosures of which are incorporated herein by reference. In addition, various energy delivery modalities have been disclosed for forming such atrial wall lesions, and include use of microwave, laser and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall, as disclosed in WO 93/20767 to Stem, et al., U.S. Pat. No. 5,104,393 to Isner, et al. and U.S. Pat. No. 5,575,766 to Swartz, et al., respectively, the entire disclosures of which are incorporated herein by reference.
In this two-step procedure—mapping followed by ablation—electrical activity at points in the heart is typically sensed and measured by advancing a catheter containing one or more electrical sensors into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the target areas at which ablation is to be performed.
Mapping and ablation in regions of or near the pulmonary veins poses special challenges due to the configuration of the ostia and surrounding tubular tissue. Catheters have been developed that are particularly useful for mapping and ablating the pulmonary veins and other tubular regions of or near the heart, including the ostium. U.S. Pat. Nos. 6,090,084 and 6,251,109 to Hassett et al., U.S. Pat. No. 6,117,101 to Diederich et al., U.S. Pat. No. 5,938,660 to Swartz et al., U.S. Pat. Nos. 6,245,064 and 6,024,740 to Lesh et al., U.S. Pat. Nos. 5,971,983, 6,012,457 and 6,164,283 to Lesh, U.S. Pat. No. 6,004,269 to Crowley et al., and U.S. Pat. No. 6,064,902 to Haissaguerre et al., all of which are incorporated herein by reference, describe apparatus for tissue ablation to treat atrial arrhythmia, primarily tissue located within the pulmonary veins or on the ostia of the pulmonary veins. Catheters having lasso, open-spine or closed-spine (basket) assemblies are also known. Such catheters are disclosed in, for example, U.S. Pat. Nos. 6,728,455, 6,973,339, 7,003,342, 7,142,903, and 7,412,273, the entire disclosures of which are hereby incorporated by reference.
“Lasso” catheters are particularly useful during circumferential ablations around the ostium of the pulmonary veins. One technique utilizes one catheter for mapping and finding abnormal potentials and a second catheter for ablating the ostium. However, during a procedure it is desirable to have continuous feedback of the potential recordings or electrograms (ECGs) inside the pulmonary vein (PV) as a circumferential ablation is performed around the vein's ostium. Having feedback of the ECGs inside a pulmonary vein during PV ostium ablation allows a user to know whether the undesired potentials have been successfully blocked by the circumferential ablation. Currently, if the user desires real time ECG feedback from inside the pulmonary vein during a circumferential ablation, a third catheter is used. Accordingly, it is desired that a single catheter be adapted to both ablate and detect potentials, and in particular, that a single catheter have both a proximal electrode assembly for ablating an ostium and a distal electrode assembly for detecting potentials in the tubular region of the ablated ostium so that it is possible to obtain ECG signals inside a pulmonary vein when ablating around the ostium.